The present invention relates to equipment for spin testing objects, such as ordnance fuse components, about a given axis of rotation. In the case of ordnance fuse components, the axis is usually equivalent to the longitudinal axis of some projectile; and the spin rate is equal to that of the projectile during flight. Such equipment is necessary to simulate flight spin conditions in the laboratory environment so that the component may be monitored during spin and/or the component may be readily inspected after spin. Flight testing is not a satisfactory method of testing these components, because it is difficult to monitor the component during flight, and because it may not permit consistent recovery of the projectile and, thus, the component in question.
Various types of ordnance projectiles experience spin rates in excess of 500 revolutions per second (rps). It has heretofore been extremely difficult--or even impossible--to build spin test equipment capable of attaining or exceeding 500 rps. This has been due to the design limitations imposed by bearings, drive systems, and speed step-up systems.
With respect to bearings, when the rotating member that contains the component to be tested is directly supported by bearings, the bearings will work at a differential speed rate which is exactly the same as the member itself. The spin rate capability of a given bearing is dependent on both its size and its design. The smaller the bearing, the greater is its spin rate capability; due, in part, to the lower linear speed and, in part, to lower centrifugal force imposed on the bearing components. However, greater spin rate capability is only obtained at the sacrifice of the bearings and inherent load carrying capability, both in the longitudinal direction (thrust) and in the radial direction (lateral load). Higher precision bearings or so-called high speed bearings will allow somewhat higher speeds, but, for a given size, this is by no means significant when compared to off the shelf bearings. Higher speed designs, further, will often require sophisticated and expensive cooling and lubrication systems, and, most often, provide the higher spin capability at an even further reduction inherent load carrying capability. The highest spin rate bearings are usually of the fluid type which support the spinning member on a fluid cushion subjected to shear. For example, air bearings are capable of extremely high spin rates (over 1000 rps) but at the cost of having negligible load bearing carrying capability.
There are no motor devices with sufficient power capable of direct spin rates on the order of 1000 rps except for gas or air turbines. Electric motors of sufficient power will "throw" the windings at these speeds. Piston or other forms of external/internal combustion engines also fly apart at these speeds. Large turbines of sufficient torque impose significant problems in the area of noise, safety, and the provision of sufficient drive fluid from either combustors or compressed gas tanks. Smaller turbines may not be capable of sufficient torque and cannot handle the lateral and thrust loadings.
Speed step-up systems or drives to obtain the requisite output speed are, generally, not acceptable. A belt drive system can impose significant side loadings on support bearings which may already be marginal. Further, centrifugal forces are imposed which may destroy the drive belt in short order. Gear trains create significant drag, may impose significant side loading, and, generally, are not suitable for these spin rates.